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Semaphores, Shared Memory, and Message Queues (Semaphores (Multiple…

- - - - Operation on an array of semaphores
        
        semget
        
        Creates a new one or obtains key
        
        semop
        
        changes the value of the semapther
        
        semctl
        
        Direct control of semaphore information
- - - - Used to create shared memory
        
        int shmget(key_t key, size_t size, int shmflg);
    - - Enable access by providing address
        
        void shmat(int shm_id, const void shm_addr, int shmflg);
    - - Detaches the shared memory from current process
    - - control functions, takes an id a command and the structure with the modes and permissions
- - - - For unrelated processes
    - - Each block has a type
        
        Can use "look ahead"
  - - - Creates a message queue
        
        int msgget(key_t key, int msgflg);
    - - Add a message to the queue
        
        int msgsnd(int msqid, const void *msg_ptr, size_t msg_sz, int msgflg);
    - - Receives message
        
        int msgrcv(int msqid, void *msg_ptr, size_t msg_sz, long int msgtype, int msgflg);
    - - Control function
        
        int msgctl(int msqid, int command, struct msqid_ds *buf);
      - Available commands
        
        IPC_STAT
        
        IPC_SET
        
        IPC_RMID
  - - - struct my_message {
      - long int message_type;
      - / The data you wish to transfer /}